1. Field of the Invention
The present invention relates to a process for preparing a silica-titania catalyst, and more specifically, it relates to a process for preparing a silica-titania solid acid catalyst for use in various kinds of industrially useful esterification reactions.
2. Description of the Related Art
Silica-titania catalysts (hereinafter referred to sometimes as "silica-titania solid acid catalysts") have been manufactured by usual preparation methods for solid catalysts such as an impregnating method, a kneading method, a co-precipitation method and a sol-gel method.
The above-mentioned co-precipitation method comprises dissolving a silicon compound and a titanium compound, and then adjusting the pH of the mixture to co-precipitate the silicon compound and the titanium compound. In the preparation of the silica-titania catalyst by this method, the silicon compound and the titanium compound which are relatively inexpensive can be used as starting materials, and the preparation of the catalyst is relatively easy. For these reasons, the co-precipitation method has often industrially been employed.
However, when the silica-titania prepared by the conventional co-precipitation method is used as a catalyst for an esterification reaction or the like, its activity is low, and for this reason, this kind of silica-titania catalyst is not satisfactory for an industrial use. In order to improve the catalytic activity, Japanese Patent Publication No. 53418/1981 has suggested a method in which a crystalline cellulose is used as a precipitation auxiliary for the silicon compound and the titanium compound. However, this method requires the use of a large amount of the crystalline cellulose, which leads to a low volume efficiency at the time of the catalyst preparation and a high manufacturing cost, and in addition, the activity of the obtained silica-titania catalyst is not so high. In consequence, the thus obtained catalyst is not satisfactory as the industrial solid acid catalyst for the esterification reaction or the like.